1. Field of the Invention
The present invention relates to a burner and method for burning a low calorific gas and, more particularly, to a burner and method for burning a low calorific gas having a calorific value lower than about 800 kcal/Nm.sup.3.
2. Description of the Prior Art
A variety of by-product gases come from petrochemical plants, petroleum refineries, and iron mills. Of these, high calorific ones are utilized as a heat source for heating furnaces and boilers but low calorific ones having a calorific value lower than 800 kcal/Nm.sup.3 involve difficulties in combustion. In actual practice, with a calorific value lower than 600 kcal/Nm.sup.3, they do not burn continuously because they cannot sustain the theoretical combustion temperature even when heated above their ignition point.
For this reason, the low calorific by-product gases are burned after mixing with a high calorific gas (such as butane, natural gas, and coke-oven gas), thereby increasing the calorific value to at least 800 kcal/Nm.sup.3, or burned together with a high calorific gas, fuel oil, or kerosene, in spite of economical disadvantage. Alternatively, they are burned together with a high calorific gas in the atmosphere by means of a flare stack.
There is a method for burning a low calorific gas by means of a burner provided with a heat exchange function which utilizes the combustion gas for the fuel gas preheating. There is another method for burning a low calorific gas by the aid of oxygen-enriched combustion air.
There are three methods for burning a low calorific gas. The first one employs a burner having a heat exchange function for fuel gas preheating with combustion gas. The second one resorts to oxygen-enriched combustion air. The third one involves the mixing with a high calorific gas and the preheating of both or either of the combustion air and fuel gas (as in hot stoves for blast furnaces) .
Burning a low calorific gas together with a high calorific gas (such as butane, natural gas, and coke-oven gas) or by the aid of oxygen-enriched combustion air is not only uneconomical but also undesirable for material and energy saving. Also, burning a low calorific gas by means of a burner having a heat exchange function needs a heat source for preheating and a complex structure for heat exchange.
In order to solve the above-mentioned problems, the present inventors had previously developed an apparatus for burning a low calorific gas and filed an application for patent. (See Japanese Patent Laid-open No. 306009/1990.)
Their subsequent investigation led to the development of a new burner and method for burning a low calorific gas without the need of mixing it with a high calorific gas.